(1) Field of the Invention
This invention relates to a coating composition of thermo-setting resins by which a coating film having excellent surface hardness, abrasion resistance, flexibility, transparency, antistatic property, dyeing property, thermal resistance, hot water resistance or the like can be formed on the surface of plastics.
(2) Description of the Prior Art
Plastic molded products have been used recently in almost every field on account of their light weight, workability and impact resistance. On the other hand, since they have the disadvantages of: weakness in surface hardness and abrasion resistance surface electrification allowing adhesion of dust and mist, and inferior thermal resistance, their practical use has not been always satisfactory.
In order to eliminate the above mentioned disadvantages, various methods for coating the surface of plastics using a hard substance have been tried. However, fully satisfactory methods have not been developed.
For example, a coating composition comprising as main constituent hydrolytic condensate of trifunctional silane such as methyltrimethoxysilane or vinyltrialkoxysilane is in commercialization and used for lenses of sunglasses. The product, however, is inferior to inorganic glass in the surface hardness and flexibility so that surface cracks occur by heating it at a temperature of more than 80.degree. C. under stress or disclosing it outdoors. Therefore such a product is not always satisfactory.
A coating composition comprising as a main constituent alkylsilane with an epoxy group has been developed so as to eliminate these defects. However, such compositions do not maintain desirable qualities over an extended period. A coating composition comprising hydrolyzate of alkyltrialkoxysilane with an epoxy group and zinc borofluoride, tin borofluoride or boron trifluoride amine complex has been developed. However, the coating possesses insufficient water resistance. A coating composition with a reinforced film having dyeing property, for example, a composition with aluminium salt of acetylacetone as a curing agent and with an epoxy resin for providing a dyeing property has been developed, but it is inferior with respect to hot water resistance (temperature 90.degree.-100.degree. C.).